This invention relates to magnetic tape cassettes, and more particularly to a magnetic tape cassette which includes a cassette casing having an upper half casing and a lower half casing and which incorporates a pair of tape winding members and a leaf spring depressing the tape winding members downwardly in the casing.
Audio or video devices employ magnetic tape cassettes for recording and reproducing signals in which a pair of tape winding structures (hereinafter referred to as winding reels), on which a magnetic tape has been wound are rotatably supported.
Magnetic tape cassettes for a VHS system video tape recorder (VTR), a Beta format system VTR, or an 8-mm VTR are designed as follows. A pair of tape winding reels formed of synthetic resin such as ABS and on which a magnetic tape has been wound are rotatably supported in a cassette casing formed by an upper half casing and a lower half casing. In the cassette casing, the tape winding reels are pushed downwardly by a leaf spring which is secured to the upper half casing.
FIG. 10 is a plan view showing the interior of the upper half casing of a conventional magnetic tape cassette for a VHS system VTR, and FIG. 11 is a perspective view of a leaf spring in the cassette.
As shown in FIG. 10, the leaf spring 60 is made of a metal plate. That is, the leaf spring includes a middle portion, namely, a fixing portion 61, and right and left arms 62 which extend from the fixing portion 61 to the right and left and which are suitably curved. The fixing portion 61, as shown in FIG. 11, has holes 63. The holes 63 are engaged, for instance, with protrusions formed on the inner surface of the upper half casing at the center thereof. The ends of the protrusions are fused by ultrasonic welding, so that the leaf spring 60 is secured to the upper half casing with its right and left arms 62 extending towards the lower half casing.
Thus, when the magnetic tape cassette has been assembled, the leaf spring 60 pushes the central portions of the upper surfaces of the tape winding reels towards the lower half casing through the end portions of the right and left arms 62.
The leaf spring 60 thus secured is made of an elastic metal plate, as was described above. On the other hand, to reduce the manufacturing cost of the leaf spring, or to facilitate the machining operation thereof, an extremely thin plate is usually employed in manufacturing the leaf spring. Hence, since a thinner metal plate is used, the resultant leaf spring has a correspondingly decreased spring pressure. However, the decrease in spring pressure is compensated for by increasing the deflection of the leaf spring.
However, in assembling the cassette, the leaf spring thus increased in deflection is liable to spring up out of the cassette because of its elasticity. Thus, as discussed in greater detail below, it is difficult to handle the leaf spring.
Generally, the magnetic tape cassette is assembled as follows. First, the upper half casing, to which the leaf spring has been secured, is temporarily placed on the lower half casing on which the magnetic tape reels have been mounted. The upper and lower half casings thus positioned are conveyed on the production line to a subsequent manufacturing station, at which the upper and lower half casings are fixedly secured together.
In this operation, a leaf spring having a large deflection creates the following difficulty. Specifically, when the upper half casing is temporarily placed on the lower half casing, the elasticity of the leaf spring on the magnetic tape reels urges the upper half casing so as to raise the upper half casing above the lower half casing, so that the upper half casing may be displaced, or even completely separated, from the lower half casing. Thus, it is difficult to combine the upper half casing with the lower half casing with high accuracy.
The above-described difficulties may be eliminated by decreasing the deflection of the leaf spring, i.e., by using a leaf spring having a small depression force. However, a magnetic tape cassette with such a leaf spring is still disadvantageous. For example, when the cassette is loaded into a signal recording and reproducing device, the drive shafts of the device are inserted into the cassette from below and are engaged with the magnetic tape reels. In this operation, the drive shafts may push upwardly on the magnetic tape reels such that the drive shafts are not engaged with the tape reels. Furthermore, the drive shafts may disengage the magnetic tape reels during operation.
In view of the foregoing, an object of this invention is to provide a magnetic tape cassette in which, when the cassette is assembled or stored, the leaf spring has a relatively small elastic deflection, thus lightly depressing the magnetic tape reels, and when the cassette is loaded into a signal recording and reproducing device, the leaf spring has a sufficiently high spring pressure to allow the drive shafts of the signal recording and reproducing device to positively engage the magnetic tape reels.